The critical path method is a predictive project management methodology that can help project managers determine how long a project will take to complete. In addition, it can improve scheduling, enhance resource planning and help mitigate risks and scope creep. All of this sounds like a dream come true, but if used incorrectly, this complex methodology can land a project team in all sorts of trouble.
In this guide, I’ll cover what the critical path method is and how it works. I’ll explain how to find the critical path and how program evaluation and review technique (PERT) charts and Gantt charts can help you better understand tasks and their dependencies and visualize project timelines. I’ll even share with you the software suites that will make your life easier. By the end of this guide, you’ll be a critical path method ninja who can plan projects with ease.
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What Is the Critical Path Method (CPM)?
The critical path method (CPM), which is also known as critical path analysis (CPA), is a project management methodology that allows project managers to identify and manage the longest sequence of tasks and their dependent tasks that are critical for project completion.
The tasks on the critical path are considered critical because if any of the tasks aren’t completed on time, the whole project will be delayed, which will lead to scope creep and unhappy stakeholders and clients. While the critical path method is one of the best methodologies for large projects, you must understand that it is also one of the most complex project management techniques and should not be used by those who do not have a full understanding of how it works.
Why Use Critical Path Analysis (CPA)?
The critical path analysis is the perfect method for project managers who need to not only identify critical tasks, but also who need to:
- Enhance planning. You’ll find that projects that benefit from CPA will have many repeatable phases. Once you have familiarized yourself with CPA, you can take what you learn and apply it to future projects without much fuss.
- Improve resource management. The critical path enables better resource management. Knowing when tasks will be taking place allows managers to improve resource planning and ensure required resources are ready at the right time.
- Mitigate risks and bottlenecks. Understanding project tasks and dependencies can help managers identify risks, such as resource and supply problems. The critical path also makes it easier to see bottlenecks, meaning you can address them before they occur.
How To Find the Critical Path
Finding the critical path is nothing more than finding the longest sequence of events between the project’s start and end dates. Below, I’ll walk you through the steps you need to take to find the critical path for any project.
1. Determine Project Tasks
The first step in the process is to determine all the tasks that will need to be finished to complete the project. The best way to do this, especially for large, complex projects, is to use a work breakdown structure (WBS). A WBS allows a project manager to break down large projects into small, bite-sized stages and tasks that won’t overwhelm the project team.
Let’s take a look at a project for a new movie. The movie’s project manager might break down the project into tasks like this:
| Task ID | Task Description | Task Duration |
|---|---|---|
| A | Scriptwriting | 2 weeks |
| B | Create story boards | 3 weeks |
| C | Shooting | 3 months |
| D | Editing | 3 months |
| E | Final review | 4 weeks |
When the project has been broken down into phases and tasks, you can start to assign the tasks to team members, add start and end dates, start resource planning and determine which tasks will be dependent on others.
2. Identify Task Dependencies
A vital step in defining the critical path of a project is determining task dependencies. Continuing with our movie project, you can determine that the following tasks are dependent on each other:
- Task B is dependent on task A, as storyboards cannot be created without a script.
- Task C is dependent on tasks A and B, as shooting cannot start without a script and storyboards.
- Task D is dependent on task C, as editing cannot be started until filming is complete.
- Task E is dependent on task D, as a review cannot take place until editing is finished.
Once you have determined task dependencies or activity sequence, you will be able to create your project’s critical path.
3. Draw a Critical Path Diagram
Once tasks and dependencies have been determined, it’s time to create a diagram of your project’s critical path. The diagram is nothing more than a flow chart. You can use a piece of paper, a whiteboard or project management software, including some of the platforms listed in our roundup of the best free project management software to draw the critical path. No matter what you use, add tasks to the diagram until your project is plotted.
4. Calculate Task Durations
Determining the tasks that make up your project is only part of the critical path equation, as you also have to define how long you think each task will take to complete. Defining how long a task will take is guesswork, but you can lean on past experiences or industry norms to help determine a task’s length. If pulling numbers out of the air isn’t your cup of project management tea, you can use one of the following techniques:
- Forward pass. Allows you to calculate the earliest possible start and finish dates. The dates will be based on a previously determined start date. For example, if task C starts on the 12th and you estimate that it will take three days to finish, you can calculate that the earliest start date (ES) for task D will be the 15th, and if task D takes four days to finish, you can determine that its earliest finish date (EF) will be the 19th. This method allows you to start planning project resources effectively.
- Backward pass. Allows you to determine the latest possible task start (LS) and finish (LF) dates. To use this method, you look at the last scheduled critical path activity or task and then work your way backward down the critical path.
5. Assign Float (Slack) to Each Task
An important part of creating your critical path is building in float, or slack time, for each task. The float time is extra time that a task can take to complete without completely derailing subsequent tasks, and, therefore, the whole project. In simple terms, float is flexibility. To calculate a task’s float time, you can use a simple formula:
- Float (slack) time = Latest start date (LS) – Earliest start date (ES).
If you really want to get into the weeds and be as precise as possible, you can choose to use total float or free float.
- Total float. This refers to the total amount of time from the earliest start date (ES) that a task can be delayed without impacting the overall project’s end date. The equation for total float is: Total float = LS – ES or LF – EF.
- Free float. This type of float refers to the amount of time a task can be held back without having a direct impact on the next task in the sequence. The equation for free float is: Free float = Earliest start date (ES) of the next task – Earliest finish date (EF) of the current task (ES – EF).
6. Calculate the Critical Path
It’s time for some more math. Don’t worry, you don’t need a degree to calculate the critical path. Just follow these steps.
1. Determine Project Duration
Simply jot down the start date of the first task in your sequence and note the date of the last task in the sequence. The length of your project is the ending date of the last task, minus the starting date of the first task.
2. Count Dependencies
Look at your critical path diagram and count the number of dependencies in each sequence.
3. The Critical Path Is Yours
At this point, you should be able to see the sequence of project events that will take the longest amount of time to complete. This is the critical path. If you find that you have multiple sequences with the same duration, don’t panic. The answer to this quandary is that the sequence with the most dependencies is the critical path. That’s it. You did it. You have determined your project’s critical path. Take a deep breath and revel in the glory.
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Critical Path Method Example
Now that you know what the critical path is and how to find it, let’s take a look at an example of a critical path. For this simple example, we’ll imagine that we are creating a video for a popular streaming platform. We’ll identify our tasks, determine dependencies and decide which tasks are critical to the project’s success. We’ll also determine which tasks can run in parallel and produce our critical path diagram.
Identify Tasks
Tasks for creating our video include:
- Writing a script
- Securing a filming location
- Gather props
- Choose outfits
- Shooting main video
- Capture B-roll
- Editing video
- Add graphics, music and voice-overs
- Review the final product
- Publish
In the list above, there will be tasks that cannot start until another task is complete (dependencies). We also know that not every task listed is critical and can be placed parallel to the critical path. The noncritical tasks, which will not have an impact on the project’s end date, can be completed at the same time as critical tasks.
For example, gathering props and choosing outfits can be done at the same time as securing a location for filming. When producing your critical path diagram, the noncritical tasks are placed parallel to the critical path, which you will see in the next section.
Producing a Critical Path Diagram
As previously mentioned, you can use a variety of media to create your critical path diagram. I recommend using a project management platform, such as those found in our roundup of the best project management software, as they make it easy to update and share diagrams with team members, key stakeholders and clients. For this example, I used a mind map in ClickUp and highlighted the project’s critical path in green.
Remember, the critical path is made up of tasks that are critical to the success of the project and that represent the longest sequence to complete the project. The critical items are all dependent on the task before being finished, while the items that are placed parallel to the critical path generally won’t affect the project’s completion date.
The great thing about using project management software is that, while you are creating your critical path diagram, you can also plot the tasks on a Gantt chart and have a visual representation of the project’s timeline. You can also keep track of tasks on kanban boards. These tools make it painless to add task assignees and task start and end dates.
This example is an incredibly simple example of a critical path project, but it should show you how easy it is to create a critical path diagram using project management software. In no more than 10 minutes, I was able to identify tasks, determine dependencies, create a diagram, determine start and end dates and assign tasks to members of my team.
When Should You Use the Critical Path Method?
Project managers should use the critical path method (CPM) when:
- Working on complex projects
- Managing projects with strict deadlines
- Overseeing resource-intensive projects
- You expect to work on similar projects in the future
- Working on projects that cannot afford to fail or succumb to scope creep
What Industries Use the Critical Path?
The critical path method has been used to manage projects in construction and manufacturing industries for a long time, but it is now favored by project managers working in:
- Research and development
- Aerospace and defense
- Event planning
- Financial planning
- Product launches
Critical Path Method Pros and Cons
The critical path method has many pros and plenty of cons. Before you start using this classic project management methodology, it would be wise to understand its advantages and disadvantages.
Critical path method pros:
- Improves project planning
- Enhances communication with stakeholders and clients
- Highlights risks and bottlenecks
- Helps keep projects on time and budget
- Enhances project scheduling
Critical path method cons:
- Relies on estimates, which could lead to unrealistic timelines and delays
- Does not take resource constraints into account
- Not suitable for projects with any level of uncertainty
- Isn’t very flexible and can be hard to update once the project has started
- Can become overly complex for very large projects, which can lead to errors
PERT Charts, Gantt Charts and CPM
If you choose to use the critical path method, you’ll likely run into PERT charts and Gantt charts. While the critical path is a full-blown methodology that can help with planning, organizing and managing entire projects, and provides built-in solutions to help you find the critical path, you can use other tools and techniques (PERT charts and Gantt charts) to make your life easier.
“The difference between the two methods is that while the Gantt chart dramatically represents time in a unit execution, PERT shows the relation of tasks, variable timing and uncertainties of accomplishment. Gantt charts allow easily for the organization of structured projects with bounded time periods while PERT is clearly best suited to analyze the confusing world of uncertainty,” says Mircea Dima, founder of AlgoCademy, an online coding school.
Let’s take a closer look at PERT charts and Gantt charts.
PERT Charts
A PERT chart is a tool that project managers can use to help them better understand project tasks and their dependencies. With a PERT chart, you can define optimistic (O), pessimistic (P) and most likely (M) time frames for individual tasks and their dependencies to better estimate a project’s timeline. When used correctly, PERT charts can help project leaders find a project’s critical path.
Gantt Charts
Gantt charts are a tool in a project manager’s arsenal that can help them visualize project timelines. Once a critical path has been identified, tasks and their dependencies can be plotted onto a Gantt chart. The charts can be shared instantly with team members, clients and stakeholders so that they can see what will happen and when. If you need a way to create Gantt charts, our roundup of the best Gantt chart software is for you.
Critical Path Method and Project Management Software
While you can manage a project from a whiteboard and sticky notes, there’s simply no need to these days, especially when the best project management software is affordable and when you can get your hands on capable free project management software. Below, I have listed the three best project management software suites to use for critical path projects.
- ClickUp. With intuitive Gantt charts, collaborative whiteboards, mind maps, docs, and plenty of task management tools, ClickUp is the software we recommend to most project teams. Not only does it offer a robust feature set, but it also offers a stout free plan and affordable paid options. Learn more in our full ClickUp review.
- Monday.com. If you’re new to project management software, Monday.com is the place to be. Its tools, including Gantt charts, are user-friendly, its menus are easy to navigate and project templates can get you started quickly. Learn more in our full Monday.com review.
- Teamwork.com. Gantt charts, resource management tools and robust collaborative documents make Teamwork.com the ideal platform for teams managing and working on critical path projects. Teamwork.com offers a robust free plan and there are paid plans to suit most budgets. Learn more in our full Teamwork.com review.
The Bottom Line
The critical path method is a fantastic project management methodology that can help project managers determine how long a project is going to take to complete. When used in conjunction with PERT charts and Gantt charts, project leaders who lean on the critical path method can better understand the relationship between project tasks and dependencies, risk mitigation and resource management. While the critical path method isn’t suitable for small projects, its ability to help project teams get to grips with complex projects must be praised.
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Frequently Asked Questions (FAQs)
How do you calculate the critical path in a project?
To calculate the critical path in a project, you must first identify all project tasks and task dependencies and estimate how long each task will take to complete. Once you have determined what sequence of events has the longest duration to completion, you will have discovered the project’s critical path.
What are the benefits of using the critical path method?
The benefits of using the critical path method include enhanced scheduling and time management, improved risk and resource management, a lower risk of scope creep and better communication with clients and stakeholders.
How does the critical path method differ from PERT and Gantt charts?
The critical path method is a full-blown project management methodology that dictates how a project should be executed from start to finish, while PERT and Gantt charts are techniques and tools that can help managers determine and visualize the critical path.
What tools can help implement the critical path method?
To implement the critical path method, you can use project management software to organize and manage tasks and visualize timelines. You can also use PERT charts to help you determine the critical path by defining optimistic, pessimistic and most likely completion times for critical tasks and their dependencies.
Can you provide an example of the critical path method in action?
An example of the critical path method would be to look at making an espresso-based drink and the longest sequence of events. The critical tasks would be grinding beans (1 minute), distributing grounds (30 seconds), tamping grounds (30 seconds) and pulling the shot (30 seconds). The longest sequence of tasks would be two minutes and thirty seconds. This is the critical path, as you cannot have an espresso-based drink without a shot of espresso. Tasks, such as adding milk and syrups, would be tasks that run parallel to the critical path.
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